This invention relates to an improved hair straightening system and a pre-shampoo normalizer for use in a hair straightening system.
Among the components of hair is a proteinaceous material called "keratin". The hair's keratin is made up of long fibrous polypeptide chains which are in turn formed from amino acids. The fibrous polypeptide chains are bonded together with horizontal cross bonds of two forms: hydrogen bonds and cystine bonds, also sometimes referred to as disulfide bonds.
Cystine bonds play an essential role in determining the degree of curl in hair. Straight or slightly wavy hair has very few cystine bonds and relies heavily upon hydrogen bonding to produce curl or waves in the hair. Very curly hair has a relatively larger amount of cystine bonds in the hair. While the hydrogen bonds can be broken merely by wetting the hair, such that straight or slightly wavy hair will lose virtually all body when wet, very curly hair maintains its body even when wet because the cystine bonds are relatively unaffected by water. Thus, very curly hair cannot be easily reset into new or different hair styles different from its natural state merely by wetting and shaping the hair.
In order to style very curly hair, the hair must first be straightened to some degree. This procedure is commonly referred to in the trade as "straightening" the hair. A composition employed to straighten the hair is similarly called a straightener or "relaxer." Straighteners have become increasingly popular in recent years with the emergence of hair styles that require straight or only slightly wavy hair.
The most important factor in hair straighteners is chemically breaking the cystine bonds so that the bonding sites may then slip past one another, permanently shifting their position and that of the polypeptide chains. The bonds may then be reformed at new bonding sites with the result that the hair assumes a relatively permanent straight position.
Alakline chemicals are typically used to break the cystine bonds. The alkaline chemicals also have the effect of softening and swelling the hair fiber. If the chemical is left on the hair for too long a period of time or if the chemical is too strong or too abundant, it may not break the cystine bond but also weaken or even dissolve the hair fiber. The outwardly visible sign of this type of chemical damage is destruction or breaking off of the hair.
There has been much discussion, often misleading, in recent literature about the pH of hair. Contrary to popular belief, hair has no intrinsic pH. However, the scalp and natural oils coat the hair fiber, giving its surface a slightly acidic pH of between about 4.5 and 5.5. In addition, hair has positive and negative charges which are balanced at a point known as the "iso-electric point." The iso-electric point generally falls in the range of about 5.0 to 6.5 on the pH scale.
Mildly acidic compounds, such as rinses and conditioners, etc., tend to shrink the hair fiber and flatten the cuticle, leading to a smoother appearance and reduction in comb drag. More strongly acidic compounds tends to have an increasingly damaging effect on hair. Similarly, mildly alkaline compounds swell and soften the hair fiber, permitting easier penetration of cosmetic ingredients into the hair. More strongly alkaline compounds are, again, damaging if left on the hair for too long and may even dissolve the hair.
It is believed that the most widely used chemical hair straightener currently employed is sodium hydroxide, although other compounds such as thioglycolates, bisulfides or other hydroxides, may also be used. Sodium hydroxide is a highly alkaline chemical and has various advantages in connection with straightening very curly hair; namely, fast processing time, good straightening, and more permanent straightness with less likeihood of reversion after shampooing. However, in view of the highly alkaline nature of sodium hydroxide, extreme care must be used in order to avoid damaging the hair, skin, or scalp. If the chemical is left on the hair for much longer than the recommended time, the hair can become brittle. In a brittle condition, the hair may be damaged by normal shampooing upon completion of the straightener treatment.
The prior art has taught various techniques for using selected compositions in a way that conditions the hair and reduces the risk of damage to hair as a result of contact with the straightener compositions. In addition to reducing the risk of damage, such compositions frequently add an aesthetic quality to the hair, e.g., easier combability, softer touch, higher sheen. For example, it has been known that cationic fatty quaternary compounds having fatty chain length of approximately 8-18 carbon atoms may help condition hair. However, since such cationic materials are usually inactivated by reaction with anionic surfactants, they have typically been employed as separate rinse treatments after shampooing. U.S. Pat. Nos. 3,313,734 and 3,761,417 purportedly describe improved conditioning compositions which could be incorporated into a shampoo. Such incorporation is said to minimize hair damage of shampooing following straightening because the conditioner would begin to contact the hair fiber before the hair had been seriously manipulated and damaged during the shampoo process. More recently, as taught by U.S. Pat. Nos. 3,912,808; 3,986,825; and 4,027,008, it was known that certain tertiary amine polymers and quaternary ammonium polymers could be incorporated directly into the straightening or hair treatment composition and, thus, could begin to condition the hair and reduce potential damage to the hair even before shampooing. Still later patents, for example, U.S. Pat. No. 4,175,572, disclosed that specific quaternary ammonium polymers could be employed in a wider range of straightener compositions having a higher pH than was previously known.
All of the known prior art techniques for reducing damage to the hair in a straightener system are very limited in their ability to prevent damage to the hair. Although prior art compositions have shown some utility in this regard, relaxers and hair straightening techniques are still plagued by problems of hair damage and introduction of a harsh or raspy feel to the hair. The present invention provides an improvement in hair straightener systems, further reducing the likelihood of damaged hair and further improving the hair styling that results from a hair straightening treatment.